Communication devices such as mobile phones have widened their functions including connection to the Internet. To address the increase of communication data, development of technologies such as LTE (Long Term Evolution)-Advanced has been promoted. In the LTE-Advanced system, CA (Carrier Aggregation) is used to obtain high throughput. For example, Inter Band Non Contiguous CA is a technique to widen the band, increase the speed, and increase an amount of data by sharing two or more frequency bands such as an 800 MHz band and a 2 GHz band. For example, two signals such as a video and a sound or a sound and data can be simultaneously transmitted and received. Or, two signals may be simultaneously transmitted only, or simultaneously received only.
To support two or more frequency bands, used are duplexers with different passbands and a switch that switches the duplexers. This enables to support communication methods of two or more countries and areas. For example, International Publication No. 2010/024376 discloses a technique that connects a resistance to a port of a switch using an FET (Field Effect Transistor). Japanese Patent Application Publication No. 2008-48450 discloses a module to which a switch and a diplexer are connected. Duplexers are connected to a diplexer through the switch. Thus, signals of different communication methods can be transmitted and received.
For example, when signals of two communication systems are simultaneously transmitted and received, two duplexers are coupled to the diplexer. Good frequency characteristics can be obtained by impedance matching. When a first signal of the two signals is transmitted and received, one duplexer is coupled to the diplexer. At this time, to block a second signal, the switch is turned off. The switch in an off state has, for example, an open impedance. Or, a first end of the switch is grounded to enhance a switch off state. In such cases, the impedance deviates from, for example, 50Ω, and thus it is difficult to match the impedance of the diplexer having a port of which the impedance is designed to be 50Ω, and the insertion loss may increase.